Method and apparatus for characterizing movement of a mass within a defined space

Abstract

Apparatus and methods for resolving movement of a mass within a defined space utilizes at least one electrode proximate to the space to be observed. An AC signal is applied to the electrode, and the current measured from that electrode and also to any other electrodes included in the system and which are effectively connected to the ground return of the AC-coupled electrode. A person (or object) to be sensed intercepts a part of the electric field extending beween the AC-coupled "sending" electrode and the other "receiving" electrodes, the amount of the field intercepted depending on the size and orientation of the sensed person, whether or not the person provides a grounding path, and the geometry of the distributed electrodes. Given the nonlinear spatial dependence of the field, multiple electrodes can reliably distinguish among a set of expected cases. The invention detects motion by taking sequential measurements at different times and utilizing the time variation in signal magnitudes as well as the absolute magnitudes themselves.

What is claimed is: 
     
       1. Apparatus for characterizing movement of a mass within a defined space, the apparatus comprising: a. at least one electrode proximate to the space;   b. an AC source;   c. means for sequentially connecting each of the at least one electrode to the AC source at fixed intervals so as to produce a plurality of electric fields;   d. means for measuring current flowing from the electrode that is connected to the AC source; and   e. means for characterizing movement of the mass within the space based on the measurements.   
     
     
       2. The apparatus of claim 1 further comprising: a. a computer memory for storing (i) the measurements and (ii) a pattern of measurement clusters each associated with a movement; and   b. a processor for comparing the measurements against the pattern to thereby characterize movement of the mass.   
     
     
       3. Apparatus for characterizing movement of a mass within a defined space, the apparatus comprising: a. at least two electrodes proximate to the space, the electrodes having fixed positions relative to each other;   b. an AC source;   c. means for momentarily connecting at least a first electrode to the AC source a plurality of times so as to produce a plurality of electric fields;   d. means for measuring current flowing into at least one unconnected electrode each time the first electrode is connected to the AC source, thereby producing a plurality of measurements; and   e. means for characterizing movement of the mass within the space based on the plurality of measurements.   
     
     
       4. The apparatus of claim 3 comprising at least three electrodes, the connecting means being configured to sequentially connect each of the electrodes to the AC source, and the measuring means being configured to make at least two measurements of current flowing into one of the unconnected electrodes and at least one measurement of current into another of the unconnected electrodes. 
     
     
       5. The apparatus of claim 3 comprising at least three electrodes, the connecting means being configured to connect a first of the electrodes to the AC source, and the measuring means being configured to make at least two measurements of current into a second of the electrodes and at least one measurement of current into a third of the electrodes. 
     
     
       6. The apparatus of claim 3 further comprising: a. a computer memory for storing (i) the measurements and (ii) a pattern of measurement clusters each associated with a movement; and   b. a processor for comparing the measurements against the pattern to thereby characterize movement of the mass.   
     
     
       7. A method of characterizing movement of a mass within a defined space, the method comprising the steps of: a. providing at least one electrode proximate to the space;   b. sequentially transmitting an AC signal through the at least one electrode at fixed intervals so as to produce a plurality of discrete electric fields separated in time;   c. measuring current flowing out of the electrode each time the AC signal is sent; and   d. characterizing movement of the mass within the space based on the measurements.   
     
     
       8. The method of claim 7 wherein the mass is a person. 
     
     
       9. The method of claim 7 wherein the characterization step comprises the substeps of: a. providing a pattern of measurement clusters each associated with a movement; and   b. comparing the measurements against the pattern to thereby characterize movement.   
     
     
       10. A method of characterizing movement of a mass within a defined space, the method comprising the steps of: a. providing at least two electrodes proximate to the space, the electrodes having fixed positions relative to each other;   b. momentarily transmitting an AC signal through a first electrode a plurality of times so as to produce a plurality of discrete electric fields separated in time;   c. measuring current flowing into at least one unconnected electrode each time the signal is transmitted by the first electrode, thereby producing a plurality of measurements; and   d. characterizing movement of the mass within the space based on the plurality of measurements.   
     
     
       11. The method of claim 10 wherein the characterization step comprises the substeps of: a. providing a pattern of measurement clusters each associated with a movement; and   b. comparing the measurements against the pattern to thereby characterize movement.   
     
     
       12. The method of claim 10 wherein the mass is a person. 
     
     
       13. A method of characterizing movement of a mass within a defined space, the method comprising the steps of: a. providing at least one electrode proximate to the space;   b. sequentially transmitting an AC signal through the at least one electrode at fixed intervals so as to produce a plurality of electric fields;   c. measuring current flowing from the electrode as the AC signal is sent; and   d. characterizing movement of the mass within the space based on the measurements by (i) providing a pattern of measurement clusters each associated with a movement, (ii) comparing the measurements against the pattern, and (iii) based on the comparison, characterizing the movement.